The present invention relates generally to delivery systems for deploying medical devices and, more particularly, to delivery systems to accurately deploy medical devices, such as a stent, a vascular stent-graft and the like, in a body vessel of a patient for the treatment of stenosis, aortic aneurysms and other afflictions which may strike body lumens.
Stents are generally cylindrically shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other arterial lumen, such as coronary artery. Stents are usually delivered in a compressed condition to the target site and then deployed at that location into an expanded condition to support the vessel and help maintain it in an open position. They are particularly suitable for use to support and hold back a dissected arterial lining which can occlude the fluid passageway there through. Stents are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty, percutaneous transluminal angioplasty, or removed by atherectomy or other means, to help improve the results of the procedure and reduce the possibility of restenosis. Stents, or stent like devices, are often used as the support and mounting structure for implantable vascular grafts which can be used to create an artificial conduit to bypass the diseased portion of the vasculature, such as an abdominal aortic aneurism.
A variety of devices are known in the art for use as stents and have included coiled wires in a variety of patterns that are expanded after being placed intraluminally on a balloon catheter; helically wound coiled springs manufactured from an expandable heat sensitive metal; and self expanding stents inserted into a compressed state for deployment into a body lumen. One of the difficulties encountered in using prior art stents involve maintaining the radial rigidity needed to hold open a body lumen while at the same time maintaining the longitudinal flexibility of the stent to facilitate its delivery and accommodate the often tortuous path of the body lumen.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self expanding stent formed from shape memory metals or superelastic nickel titanium alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery, or when a restraining sheath which holds the compressed stent in its delivery position is retracted to expose the stent.
Some prior art stent delivery systems for delivery and implanting self-expanding stents include an inner member upon which the compressed or collapsed stent is mounted and an outer restraining sheath which is initially placed over the compressed stent prior to deployment. When the stent is to be deployed in the body vessel, the outer sheath is moved in relation to the inner member to “uncover” the compressed stent, allowing the stent to move to its expanded condition. Some delivery systems utilize a “push pull” type technique in which the outer sheath is retracted while the inner member is pushed forward. Another common delivery system utilizes a simple pull back delivery system in which the self expanding stent is maintained in its compressed position by an outer sheath. Once the mounted stent has been moved at the desired treatment location, the outer sheath is pulled back via a deployment handle located at a remote position outside of the patient, which uncovers the stent to allow it to self expand within the patient. Still other delivery systems use an actuating wire attached to the outer sheath. When the actuating wire is pulled to retract the outer sheath and deploy the stent, the inner member must remain stationary, preventing the stent from moving axially within the body vessel.
In certain applications, it is desirable to employ a delivery system which provides a low profile to allow the catheter portion of the system to reach tight distal lesions. For such applications, the stent delivery catheter is required to have a relatively low profile to facilitate positioning the operative distal end portion of the catheter at the desired treatment site in the patient's body lumen. Delivery system can attain a reduced overall profile by utilizing tubular components having a small diameter to create the catheter portion of the delivery system. However, the delivery system will still require the use of components that provide sufficient pushability or axial stiffness to allow the catheter portion to be delivered over a guide wire to the target location. For example, a catheter with a distal shaft section having a large wall thickness likely has sufficient catheter tensile strength to be pushed along a guide wire to a target location in a patient's vasculature, however, it may not have sufficient flexibility and low profile/lumen size to be practicable in all applications. If the catheter shaft does not possess sufficient pushability, then the physician may have a difficult time reaching the target lesion. The catheter profile must be balanced with competing considerations such as the catheter tensile strength and kink resistance, and other important characteristics such as those related to the nature of the materials used to form the catheter components. When downsizing catheter components to reduce the overall profile of the catheter, the size of the components must still be strong enough to supply the pushability and kink resistance needed for a given application. Accordingly, while it is desirable to reduce the profile of a delivery system, the delivery system's pushability should not be compromised. Therefore, what has been needed is a stent delivery catheter system with an improved balance of these catheter characteristics.
Some delivery systems which utilize an inner catheter member to support or carry a medical device obtain the necessary axial strength by rely on lengths of tubing having different axial strengths. In this regard, the more proximal sections of the inner catheter member utilize tubing which has increased axial strength to allow the physician to push the catheter portion of the delivery system through the body vessel. The more distal section of the inner catheter member is usually made from a much more flexible tubing to provide needed flexibility at the distal end which often is placed in tortuous and narrow body vessels. As a result, the inner catheter member is often made from a number of different tubular sections bonded together to create a composite unit. From a manufacturing standpoint, the bonding of different tubular sections together increases the overall cost of the product since such bonding steps can often be labor intensive. Additionally, there is always a possibility that the catheter could tear as the physician is pulling the catheter from the patient.
The manufacturing of stent delivery systems also often require the physical attachment of small components together to create a composite catheter. For example, atramatic catheter tips, often attached at the distal most end of the catheter portion of a delivery system, provide a soft component that helps to prevent trauma to the vessel walls as the catheter portion is being delivered through, for example, the patient's vasculature. Delivery systems that do not include a distal tip at the end of the catheter portion can cause a “snow-plowing” effect as the distal tip scrapes against the vessel walls. The scraping of the distal end of the catheter portion can cause significant damage to the vessel walls and could promote the formation of plaque at the damaged locations. Soft distal tips can prevent this from occurring and thus are quite useful to a stent delivery system or any delivery system which is delivered into a body vessel. However, the distal tip must remain permanently attached to the catheter portion. A catheter distal tip which becomes un-attached within the body lumen can cause extreme trouble to the physician performing the medical procedure. For example, a catheter design having insufficient tensile strength can result a catheter failure as the catheter is under tension while being proximally retracted from within the patient's body lumen, such that the catheter shaft partially or completely tears, which can result in the potentially lethal dislocation of the catheter distal tip. Therefore, there is also a need to maintain the distal tip permanently bonded to the catheter on any delivery system.
The present invention disclosed herein satisfies these and other needs.